Sample identification is important to many commercial industries. The ability to quickly, cheaply, and accurately determine an unknown sample is important in diverse applications ranging from drug discovery to alarm systems. Scientific researchers also make use of sample analysis, for example to conduct genetic research, analyze pollutants in the atmosphere and to monitor processes, such as vapor deposition processes. Scientific researchers and commercial industries continue to find needs for sample identification and analysis.
The intensity of a porous thin film's, e.g., porous silicon, visible photoluminescence changes depending upon the types of gases absorbed to its surface. This phenomenon constitutes the basis for a simple and inexpensive chemical sensor device (See, U.S. Pat. No. 5,338,415). Methods exist to chemically alter porous silicon's surface, and porous silicon can be tuned to be sensitive for specific gases and liquids. Also see, e.g., “Investigation of Porous Si for Vapor Sensing” Anderson, R. C.; Muller, R. S.; Tobias, C. W., Sensors and Actuators 1990, A21-A23, 835-839; “Porous Silicon as a Material in Microsensor Technology” Barret, S.; Gaspard, F.; Herino, R.; Ligeon, M.; Muller, F.; Ronga, I. Sensors and Actuators A 1992, 33, 19-24; and “Proton Gated Emission from Porous Silicon” Chun, J. K. M.; Bocarsly, A. B.; Cottrell, T. R.; Benziger, J. B.; Yee, J. C. J. Am. Chem. Soc. 1993, 115, 3024-3025. Porous silicon thin film's, e.g., porous silicon, insulator and semiconductor films, can be fabricated to display well-resolved Fabry-Pérot fringes in their luminescence and reflection spectra. Such interference-based spectra are sensitive to gases or liquids adsorbed to the inner surfaces of the porous Si layer. U.S. Pat. No. 5,318,676 uses the interference based spectra to identify adsorbed individual gases or liquids. U.S. Pat. No. 6,248,539 used a binder to bind analytes in pores and then identify the analytes by detecting a shift in the reflection spectra.
There continues to be a need for fast, sensitive and inexpensive sample analysis devices. A particular need exists for devices capable of detecting constituents in liquid and gas mixtures.